In recent years, touch panels have been used in apparatuses such as smartphones and tablet terminals. A touch panel allows a person to perform page turning, enlarging, and reducing of an image displayed on a screen with a pointing operation in accordance with intuition of the person. Meanwhile, projectors (projection display units) have been known for a long time, as a display unit that displays an image by projecting the image onto a screen. Techniques of adding a detection function such as a touch panel to a projector have been proposed (for example, PTL 1 and PTL 2).